While the pattern rule is made drastically finer in the recent drive for higher integration densities and operating speeds in LSI devices, the deep-UV lithography using KrF or ArF excimer laser light is currently utilized as the mainstream micropatterning technology. Since the deep-UV lithography using chemically amplified resist compositions is capable of processing to 0.2 μm or less, it has been industrially utilized to process a pattern with a feature size of less than 65 nm. With respect to the EB lithography, when it is combined with chemically amplified resist compositions, a practically acceptable sensitivity has been achieved despite the use of higher energy EB. The EB lithography is thus expected to have a finer processing ability. With respect to the EUV lithography, the use of chemically amplified resist compositions is believed essential for gaining a practically acceptable sensitivity.
In the course of development of such chemically amplified positive resist compositions, addition of various resist components and modifications thereof have been proposed in order to overcome many problems including resolution, sensitivity, pattern profile, PED (post-exposure delay or a change of pattern profile with standing time following exposure), and substrate poisoning. In particular, a problem that the profile of a resist pattern as developed is roughened at the edge is known as “line edge roughness” (LER), with the continuing demand for improvement in this problem. In particular, the photomask for use in photolithography must be processed to a profile having an OPC (optical proximity correction) applied thereto in order to restrain degradation of the contrast of irradiated pattern profile by light diffraction. This requires the pattern profile during processing to be substantially reduced in LER.
In the early stage, LER improvements are made by increasing both the quantities of acid generator and basic substance added. This approach alone is difficult to accommodate an attempt to form a fine pattern having a line width of less than 65 nm. Also, as the thickness of a resist film from which a resist pattern is formed is reduced to 150 nm or less, especially 100 nm or less, heterogeneous zones known as “micro-grains” are sometimes formed in the film. It is pointed out in JP-A 2010-243873 that the micro-grain is one of the causes for LER.
Methods for improving LER include pattern correction after development. JP-A 2005-19969 proposes a method of performing pattern correction after development by feeding a solvent gas to a resist pattern as developed for dissolving the resist surface. The development assembly must be equipped with a unit for feeding a solvent gas to the resist pattern and a unit for recovering the solvent gas. A method for performing pattern correction without addition of such units is by adding a minor amount of a high boiling solvent to a resist composition, forming a pattern therefrom, and heating the pattern for profile correction as disclosed in JP-A 2010-243873.